This is a revised first award that will investigate the role of adenosine in regulating blood flow in the renal medulla. The specific aims are to examine the role of cAMP in mediating A1 and A2 agonists on the diameter of isolated perfused vasa recta capillaries; 2) to determine the effects of renal ischemia on adenosine levels in the renal medulla and on medullary blood flow in vivo; 3) to determine the effects of changes in sodium diet on renal adenosine levels and regional blood flow in the kidney and; 4) to map adenosine receptor subtypes in tubular and vascular structures in the renal medulla. These studies should contribute important new information regarding the role of adenosine in the control of medullary blood flow and oxygen delivery to the renal medulla which plays a critical role in the mechanism of urine concentration, sodium and water excretion, and the control of arterial pressure.